Improvement in kiflijto obdnanoe



@einen .gte/tirs: @anni fitte.

proceed to describe it, by the aid of the drawings and of the marks'of reference denotedY thereon.

n.13. noronkiss, or neuron-ir; ugr, Letters Patent No. 73,447, elated January 2l, 1868.

die tlgchtle maar tu in tinte llttts iitcnt mit middag gaat nf ttt aan.

TO ALL WI-IOM IT MAY CONCERN:

Be it known that I, B.' B. HOTGHKISS, of the city, county, and Stateof Ilcw York, have invented certain new and useful Improvements in Riiled Cannons; and Ido hereby declare that the following is a full and exact description thereof. i

Figure 1 is a cross section through my gun near the muzzle.

Figure 2 is a corresponding section near the breech; andl Figure 3 is a longitudinal section through the entire gun on a'sma'iler scale.

The dotted line S S indicates the position of' the section seen in fig. 1. The dotted line T T indicaties the section in iig. 2. v v

Similar letters of reference indicate like parts in'all the igures. s

My invention refers to the form of the interior surface of'the gun. '.ItV is applicable to rifled guns of sizes and proportions.

By the use of my invention a less degree of friction isproduced between the gun and theprojectile. It-

follows that the projectile may be thrown further witha given charge of powder, and that' the strain on the gun is somewhat reduced. v I

To enable others skilled in the art to makeand use my invention, in the best` manner known to me, I will The material may be cast iron. "It may be moulded or cast in'the usual manner.- I producesv cylindrical hole in its interior by the ordinary means. I then proceed to cut grooves, extending longitudinallyand spirally .along the bore, by means ordinarily employed in riil'ed'. guns. The number of grooves, (of'ordina'ry riiled grooves,) as also their breadth and depth, may be varied within'wide limits. Their breadth and depthr should depend on the kind of projectile which is to be used. 4`I have-represented my gun in this drawing 'as adapted to the use of the projectile manufactured by nie,'and known as the Hotchkiss projectile. This projectile has a packing of 4soft metal, which is expanded so as to ll all the grooves in the gun very perfectly so'soon as tire is communicated to the propelling' charge of powder. l l

In my gun I produce two kinds of grooves. The iirst'kind is analogous in character to those usually known as riiied grooves. A But mine differA in one respect from ordinary ritled grooves, as will be explained below. The second kind I term relieving-grooves. Their function is not analogous .to ordinary Titled grooves. They do not like ordinar riiied rooves extend so far backvin the bore of the "un as to reach the lace lfrom which the'l y g P projectile commences itsmotion. The purpose of my relieving-grooves is to relieve the parts from friction, and not to assist in guidingl the projectile or incommunicating the ritled motion thereto.- v

My lands, or spacesmbetween the grooves, are indicated by A A, liuc., my riiied grooves by B, and my relieving-grooves by C. My riled grooves B' extend rearward from the muzzle of the gun in th'e usual manner, and terminate at or near the lli-ne to' which the'powder lills the gun-when 'the ordinary cartridge is used. My relieving-grooves C are produced along thefcentre of each groove B, and also along the centre of each land-A.

They extend rearwards from the muzzleto plane la 'little forward of the place` wherethe projectile'lies. l They may terminate by growing gradually shallower attheir rear ends, or they may terminate' abruptly; but` it 'is .very important that they should terminate finally before reaching the place where the soft Vpecking of the pro. jectile is expanded. When the powder' is ignited, its expansive` force acts violently against the rear end of 'the projectile, and induces the soft packing to envi-pand suddenly, to a limited extent, asis well understood. In ther act of so expanding, the soft packing is forced outward and tightly fills all the-*grooves which are presented at'- that point. As the projectile moves forward, the soft material, is presented to the relieving-grooves '0, but by that time the expansive action of the soft materialhas ceased, so thatit does not expand further, and therefore.-v

does not ll the relieving-grooves C.

My relieving-grooves C -are of uniform width throughout their entire length. My ril'ied grooves B are not of uniform width throughout; they are widest at the'mnzzle, arid contract in width as they proceed rearward; In order to produce this forni of my ricd grooves A, I usually subject'the gun to, two distinct riding operai tions. I `first cut my riiled grooves of uniform width from front to'v the rear. The width of theA groove thus produced is equal to the width of my riiicd groove Bat its rear end. The subsequent riding operation is for the sole purpose of widening the groove, and-consists in recutting it with the same or a dilerent'tool, so oper= ated as tocut a diifcrent spiral. I take care to so adjust thetools that the channels cut at both operations shall coincide at the rear ond 'of my rilled groove B, so that the second operation' shall have no effect at thatA point, but shall have the effect of widening the grooves at'cvery other point, widening, it'niost at the mouz-lef;

and less and *less as it proceeds rearward. -I can make the edgesof my grooves perpendicular, inclined, or l rounded to any required curve. l

I have represented my relieving-grooves C as cut considerably deeper than I usually consider necessary or desirable in practice. I have represented them deep to enable .them to be distinctly seen,- I prefer, in praetice, to make them about the width represented, and only about one sixtyfonrth of an inch deep.V I prefer t'o round both edges of the relieving-grooves C.

The rifled grooves B may be eut in the form of a true screw, but I prefer to make them with what is called an increasing twist. My relieving-grooves C may have the sametwistas the front edge B1, or they may have a greater twist, like the rear edge B2. I prefer, however, to give them a medium twist, greater than the twist of the front edge Bl and less than the twist of the rear edge B2. p

I have already stated that the purpose of my relieving-grooves C is to reduce friction without inducing any perceptible leakage of the gas. It is important that the grooves C be of considerable width, so as to materially reduce the violent rubbing'of the surface, and be, at thev same time, so shallow that a'strong current of gas shallv not enter it. A quantity of gas equalin thickness to th'e depth of the groove will of course enter each of my relieving-grooves C; but if the depth of the groove is very small, the thin stratum of gas will not be able to make its way through the shallow passage to' any'cousiderable extent. -The friction of tho gas against the stationary surface that is presented to the exterior of the thin stratum very materially retards the motion of the gas through the passage. l i Y The widening of my rifled grooves B, as the shot progresses, by giving the rear edgeiBi a quicker twist than the front edge Bl, may attain an end Acorresponding closelyto that attained by the relieving-groove C. As the projectile moves forward in the gun, it invariably pressesv against tho .front edge B very firmly. In case my riiled. grooves are uniformly wide throughout, as usual, the projectile would rub with considerable force against the rear edge B2 along its whole extent. By widening the ried groove a very little, I relieve the friction. If it,l is widened very much there will be a leakage of the gas along the groove close to the rear edge 132, provided the riding is artrue screw. I therefore make the dierence between the twist of the front edge B1 and the twist of the rear edge B2 very small indeed in such guns.. But when my ried 'grooves are eut with the increasing twist, the conditions are changed, and I then make a very considerable dii'erenee between the twist of the front edge B1 and that-of the rear edge B2. .Ido this in order to avoid or reduce thc change which must be wrought in thesoft packing of my shot in moving'along a gun thus rifled.' Inasmuch as myA soft packing assumes, at the instant ot' starting in the `gun,thc formof 'the boro. at that point where it then lies, and' of course conforms exactly to the twist which it finds at that point, it will be obvious that when. the twist is an increasing twist, and is consequently greater at the muzzle, the form which the Vpacking originally assumed cannot agree perfectly with the grooving at the muzzle. As guns are usually grooved, the soft packing of my projectile is subjected to distortion, or a continual change of shape, to adapt it to the ehangingtwistas it moves along in the gun.' My present invention avoids thiscvil; and the increasing width of my ritle'd4 grooves towards theA muzzle allows the soft packing to maintain the same form, or very'ncarly the same, as it assumed when it first received the force of the powder. The precise quantity by which I increase the width of my rifled grooves B at the muzzle, above the width et'v the same grooves near the breech, consequentlyvvaries according as the riled grooves are uniform or of an increasing twist. In case the riding is of uniform twist, I make the grooves about one sixty-fourth of an, inch wider at the muzzlethan at the back end. In case the riding has anjnereasing twist, (the twist of the front edge BS) increasing from one turn in twelve feet to one turn in ten feet, I then give to the rear edge B2 an increasing twist of an analogous character, but considerablygreater. Itv should be so much greater that each riled groove B shall be, say, about one-eighth of au inch wider at the muzzle than at its rear end. f-This is assuming that Hotchkiss projectiles of ordinary proportions are tolle used inthe gun,- and that the soft packing, after its compression, occupies about three inches of the length `of the projectile. In case the length of the soft packing shall be greater, the Vincrease in the breadth of` the ried grooves B should be greater; and in case the length of the soft packing'should be less, then the increase of the width of the riding sheuldbe less. This increase in the width of the riiled grooves towards the -muzzle4 of the gun allows the correspondingridges which are raised on the belt .of soft packing to maintain their form' about the same as was impressed onthem when 'the projectile was first started forward in the gun; and' it will be understood that the ridges of soft packing lill thegrooves near the muzzle, by reason of their standingsomewhat erosswise in the grooves at that point. In other words, tlie packing was swaged to correspond perfectly atthe point where the said ritled grooves were narrow,land they continue to ll. the grooves without changing their form when they approach the muzzle, where the grooves are wider, because they do' not here coincide in twist with the rifed grooves, but stand slightly oblique' with the grooves.l

The relieving-grooves C may be omitted in the bottom of the riedgrooves B,Iand preserved on the'lands A, or they may be Vmitted lon the lands and preserved in tliegrooves. 4I prefer to employ them in Aboth situations. i v 'i Havingnow fully described my invention, wh`at.I claim as my improvement in riding arms, and desire to secure by Letters Patent, is as follows:v

Iclam the relieving-grooves (Ll-.for the purpose herein set forth.

I B. D- HOTCHKISS. lWitnesses:

KIMBALL W. Srn'rson,

D. W. Srnrson. 

